When an automobile traveling in an urban area or the like stops to wait for a traffic light at an intersection or the like, the engine enters an idle running state, and fuel is wasted in this state. In light of this, conventionally so-called “idle reduction control” (e.g., see Patent Literature 1 to 3 below) is performed in which, if a certain condition such as the automobile stopping is established, the supply of fuel to the combustion chamber is stopped (so-called “fuel cut”), thus stopping the engine.
Also, if a predetermined engine start condition (e.g., in an automatic transmission vehicle, a brake pedal release operation or the like) is established while the engine is in the stopped state (hereinafter, this state is called the “idle reduction state”) according to the “idle reduction control”, a starter mechanism is driven, and the driving force thereof is transmitted to the engine (so-called “cranking”), thus restarting the engine and enabling startup of the vehicle. In this case, with an automatic transmission vehicle, starting up the vehicle requires turning on (engaging) a startup clutch connected to a hydraulic pressure circuit of a transmission mechanism.
With a vehicle in which such “idle reduction control” is possible, when the idle reduction state is entered, a mechanical oil pump that was operating by the driving force of the engine is also stopped, and therefore the supply of hydraulic pressure from the mechanical oil pump stops. For this reason, an electrical oil pump that can be driven by an electrical motor is provided, and even when the engine is in a stopped state, oil (hydraulic oil, i.e., ATF) is supplied to a power transmission mechanism including a transmission mechanism and the like by the driving of the electrical oil pump, thus enabling ensuring hydraulic pressure for engaging the startup clutch. In particular, with an automatic transmission vehicle, the time period from when the engine start condition (brake pedal release operation) is established until when the car starts up is shorter than in the case of a manual transmission vehicle (the engine start condition being a clutch pedal press operation), and therefore it is effective to engage the startup clutch in advance by hydraulic pressure from the electrical oil pump.
Patent Literature 1 and 2 disclose that a mechanical oil pump and an electrical oil pump are provided, and when the idle reduction state is entered, the electrical oil pump is driven and hydraulic pressure is supplied to the startup clutch, thus turning on the startup clutch. Furthermore, such patent literature also discloses a configuration in which an oil passage for directly supplying hydraulic pressure from the electrical oil pump to the startup clutch is provided, thus enabling hydraulic pressure to be supplied to the startup clutch without causing the hydraulic pressure to pass through a hydraulic pressure control unit including various types of valves (a regulator valve, a modulator valve, and the like) in the hydraulic pressure circuit. This prevents occurrences of pressure loss and oil leakage in the various types of valves.